1. Field of the Invention
The present invention relates to a paper sheet feeder for supplying a stream of single, paper, cardboard, cardstock or the like, sheets to a sheet-processing machine. With the present invention, individual sheets of paper from a pile of sheets are carried by a pile table and the uppermost sheets are supplied, singly, and in a stream, by a sheet-singling apparatus, from a conveying table to the sheet-processing machine.
2. Background Information
German Laid Open Patent Application No. 34 01 724, which corresponds to U.S. Pat. No. 4,618,135, describes a temporary-pile apparatus that is provided for the continuous operation of a sheet-processing machine, such as a printing press. The purpose of this temporary-pile apparatus is to supply the machine with sheets, from the temporary-pile apparatus, when the main pile table is empty, until a new pile of sheets has been moved into position on the main pile table, so that uninterrupted production can continue. To accomplish that, an operator must always deposit a small pile of sheets, by hand, on the temporary-pile table. Because of the continuous-stream type of sheet supply, however, with the above described temporary-pile apparatus it is possible to produce an uninterrupted continuous stream of sheets only when a switch is made from the temporary-pile apparatus to the full pile of sheets. The continuous-stream supply of sheets must, however, be interrupted when a switch is made from the empty main pile to the temporary pile.
A further disadvantage of known designs is that the temporary pile is only small in height. If thin, paper sheets are being processed in the machine, the number of sheets in the temporary pile will be sufficient for the changing and moving-into-position of a new pile of sheets. If, however, sheet stock of thick cardboard, for example, is being processed on the machine, there will be only a few sheets on the temporary-pile table and, at full machine output, these will be consumed in a very short space of time that is not sufficient for changing the pile. The machine must, therefore, be stopped or must be operated at a considerably reduced speed for the time it takes to change the pile.
If, for example, carboard with a sheet thickness of 1 mm is being processed and the machine requires, for example, 180 sheets per minute at full machine output, a temporary pile with a height of 18 cm would maintain the supply of sheets for only one minute. This short time, however, will not normally be sufficient to change the pile and to position it in the machine. Often, the piles of sheets must be brought to the machine from remote storage locations, with it not being possible, owing to the high weight of the pile of sheets, to accomplish this in just a few seconds. Also, in the case of larger sizes of sheet, a considerable expenditure of effort is required from the machine operator if, for example, he has to deposit and correctly align a 20 cm thick pile of sheets on the temporary-pile table.